1. Field of the Invention
This invention relates to a surface-joining technique requiring the deposition of metal in a protective environment, such as vacuum. More particularly, the present invention relates to a method and apparatus for manufacturing a continuous strip of laminated material.
2. Description of the Prior Art
There are many conventional methods for joining two surfaces. The use of chemical adhesives and molten bonding agents are well-known. See for example U.S. Pat. Nos. 2,691,208 and 2,965,513, issued Oct. 12, 1954 and Dec. 20, 1960, respectively, to J. B. Brennan. It is also known that two surfaces can be joined by diffusion. For example, two smooth metal surfaces prepared by machining off a few micrometers from two metal strips will bond together when placed in contact under sufficient pressure. Such bonding of metal strips by machining and rolling together in vacuum is discussed in a paper by W. C. Sherwood and D. R. Miller, "The Effect of Vacuum Machining on the Cold Welding of Some Metals," Journal of the Institute of Metals, Vol. 97, pp. 1-5, 1969. With vacuum machining, satisfactory bonding is obtained with combined strip thickness reductions of 1 to 20% as compared to 60 to 95% for conventional roll bonding in air at atmospheric pressure. The practical use of vacuum machining is limited by the difficulty of obtaining a smooth, clean metal surface, particularly when joining of wide flexible strips or non-metallic materials is desired.
A laminate can also be formed by coating a substrate with material deposited from a vapor, a molten dip or a solution. Thick layers usually require large amounts of energy and large volumes of hot corrosive materials because all the coating material must be vaporized, melted or placed in solution. Further, impervious coatings are difficult and time-consuming to obtain because of problems with adherence and pin hole imperfections.
Each of the conventional deposition methods has limitations in forming thick coatings. Vapor deposition techniques usually require cooling of the substrate in order to dissipate the heat of condensation of the thick layer of deposited material. In order to obtain a thick layer in a molten dip process, it is usually necessary that the melting temperature of the coating material be less than that of the substrate material. In electroless or electroplating processes, the choice of coating materials and solutions is severely limited, and the disposal of large amounts of toxic solutions is a problem.